A minute circuit pattern of the semiconductor integrated circuit or the liquid crystal display panel is formed using lithographic technology in which the circuit pattern is irradiated with a laser beam through a photomask and transferred onto a semiconductor wafer or liquid crystal original plate.
Formation of the circuit pattern using this lithographic technology is usually carried out in a clean room, but even in the clean room there are minute foreign particles such as dust. If the foreign particle adheres to the photomask, the particle causes reflection, shading and scattering of light, and therefore deformation and disconnection of the circuit pattern occur. In addition, edges of the circuit pattern become rough, and the ground of the semiconductor wafer or the like may be soiled. Accordingly, in order to prevent the foreign particles from adhering to the photomask, the pellicle for lithography is usually attached to the photomask.
The pellicle for lithography (hereinafter called pellicle) is comprised of a pellicle frame and a pellicle film attached to the pellicle frame. When the pellicle frame is attached to the surface of the photomask, a mask pattern region of the photomask is covered with the pellicle, and adhesion of the foreign particles can be prevented. When the foreign particles adhere to the pellicle film, the foreign particles on the pellicle film do not affect the transfer if the laser beam is focused on the mask pattern of the photomask.
In the case where the pellicle-attached photomask is used for a long period of time, a haze (growable foreign material) may be gradually generated on a mask pattern covered with the pellicle. This phenomenon occurs through photochemical reactions between gases such as organic gases, ionic gases, etc. existing in an enclosed pellicle space surrounded by a pellicle frame, pellicle film, photomask etc.
These gases existing in the enclosed pellicle space are emitted from organic materials of the pellicle and/or ion residues of the photomask. On the other hand, at the time the laser beam passes through the photomask, light scattering may occur at an edge of the mask pattern, and the pellicle frame could be decomposed through light degradation under this scattered light, thereby gases are generated in the enclosed pellicle space.
These days, circuit patterns of semiconductor integrated circuits etc. are becoming miniaturized and a shorter wavelength laser beam such as an ArF excimer laser beam (193 nm) etc. are used for the formation of the circuit patterns. Such shorter wave laser beams have high energy so that the beam tends to trigger photo reactions with these gases to cause problems such as generation of the haze.
In order to solve such problems, as shown in JP 2003-302745A, the haze on the mask pattern can be decomposed when the haze is irradiated with a laser beam over the pellicle film with the laser beam. However, even if the haze is decomposed, gases are eventually generated and remains within the enclosed pellicle space so that another haze is generated again through photochemical reactions under the laser beam.